The instant invention relates to electrostatic copiers and more particularly to a cleaning device for a fixing roll of a pressure fixing roll pair.
Conventionally, in the direct or indirect electrostatic copying process for the fixing of a developed image formed of a proper toner on a permanent record carrier, such as paper, various fixing processes may be used. According to a known fixing process, the paper sheet is passed between a heated fixing roller and a pressure roller which is in engagement with the fixing roller. During this step the powder of the toner image is melted on the paper and is caused to adhere thereto. This process, however, still has certain drawbacks. A portion of the toner sticks to the circumferential surface of the fixing roller which contacts the toner image; these adhered residues then are transferred to the paper sheet, thus causing soiling thereof. In case the temperature of the fixing roller is too low, unmelted powder adheres thereto and is pressed, in an offset-like manner, onto the successive record carriers. If, on the contrary, the temperature of the fixing roller is too high, melted powder may adhere thereto and again, soil the successive sheets. In order to prevent such an offset soiling of the paper sheets, it is necessary to carefully control the fixing temperature. Such a control of the fixing temperature is, however, fraught with difficulties.
More recently, due to the availability of new toners, another fixing process has been introduced wherein the toner image is fixed without the use of heat by means of generating a sufficiently high pressure between the two rollers. In this process too, after the pressure fixing, a certain quantity of toner remains on the circumferential surface of the fixing roller which had contacted the toner image; these toner portions have to be removed as well, since the residual toner adhering to the fixing roller would again lead to the above-noted offset soiling of the paper sheets.
It is known to arrange a silicone oil-impregnated cleaning felt in contact with the fixing roller to prevent the above-noted offset soiling. The cleaning felt is conventionally formed of a thick felt strip which is inserted in a U-shaped holder and is immobilized on both sides. It is also known, from U.S. Pat. No. 4,137,597 issued Feb. 6, 1979, to dispose a cleaning felt around a star-like frame in order to provide a plurality of cleaning felt portions. These prior art cleaning felt arrangements work well but have a limited continuous service life, necessitating frequent or occasional replacement. The instant invention provides a cleaning device for a fixing roller in an electrostatic copying machine which is capable of rendering continuous service for the full life of the electrostatic copier in which it is employed.